The research detailed in this application will concern itself principally with the mechanism of cellular immunity. A protein isolated from the sea star Asterias forbesi, sea star factor (SSF), simulates many of the effector substances released from immunized T cells exposed to specific antigen, and may be used as a probe for T cell function. While not toxic for lymphocytes in vitro, this protein inhibits the uptake of tritiated thymidine by mammalian lymphocytes in response to T cell mitogens or in mixed lymphocyte cultures. The lymphokine-like activities of this material (inhibition of macrophage migration, mononuclear chemotaxis, macrophage-activating effects, etc.) might be due either to a direct effect on mononuclear phagocytic cells or to stimulation of T cell-product synthesis. These alternatives will be examined by use of a tissue culture line of macrophages incubated in the presence of SSF, with or without the addition of T cells, or in the presence of supernatants from lymphocytes incubated with various concentrations of SSF. A similar series of experiments will examine the production of lymphotoxin by normal spleen cell exposed to SSF, and the product examined by analysis of amino acid incorporation by L cells exposed to these supernatants. The application of this material to tumor immunity will be studied, using transplantable mouse methylcholanthrene-induced tumors in attempts to investigate possible adjuvant effects when minute amounts of SSF are coupled to tumor cells for specific immunization of syngeneic hosts.